Sudden large-scale influxes of mainlanders into Hong Kong have always caused concern. From the 19th century onwards, the relative safe haven from political upheaval, and consequent hunger and chaos, which the British colony offered attracted intermittent tidal waves of people.

Amid anxiety in recent months over perceived swarms of mainland 'locusts' descending on and swiftly devouring Hong Kong's way of life, it would do us well to remember the major influx of 50 years ago. In a two-month period in early 1962, some 70,000 people crossed the frontier into Hong Kong. Most were swiftly apprehended, fed and then repatriated, but many remained.

At this time, the government's general approach towards undocumented mainland migrants was defined by the 'touch base' policy. A cornerstone of this policy allowed those who managed to evade police roadblocks and army patrols in the New Territories, and reach registration offices south of Boundary Street - and thus within 'British' Hong Kong - to stay. The 'touch base' policy remained in force until a subsequent serious illegal immigrant influx in 1980 saw it scrapped.

The border between Hong Kong and the mainland - now, for politically correct reasons, re-designated a 'boundary' - was an international flashpoint during the cold war. It was difficult to approach, and even more problematic to gain permission to cross, and most who entered Hong Kong from the mainland, in those years of constant class warfare and endless political campaigns, had no desire to go back.

But other than to escape wearisome Marxist politics, why did they come? The catastrophic failure of Chairman Mao's Great Leap Forward in 1958-60 caused a devastating famine, and desperate hunger impelled people to move in search of food. In Borrowed Place, Borrowed Time: Hong Kong and Its Many Faces, veteran Asia journalist Richard Hughes wrote that 'those who entered Hong Kong brought with them an authentic and desolate picture of a grey barren landscape of hardship and scarcity, of failing food and dwindling hope, of hungry uprooted thousands either conscripted to farm work or wandering in search of greener fields and happier lives'.

As ever, local entrepreneurialism's grasping, unlovely side reared its head; like contemporary individuals who sneak heavily pregnant women across to give birth in the hospital system's emergency wards, snake-heads smuggled desperate refugees into the colony, held them hostage until frantic relatives paid large sums to secure their release, and only then facilitated their safe transit into urban areas.

Just how many of the 1962 migrants were troublemakers sent in advance to help stir up internal security problems a few years later remains a matter for speculation. In much the same manner, exactly how many Communist Party members were brought into Hong Kong by various means in the lead-up to 1997, and for what specific long-range purposes, will probably never be clear.

'Whether intended or not,' Hughes continued, 'it served notice on Hong Kong that the Wall could not hold back engulfing waves of mainland Chinese if Peking elected to release them again. The human waves could return, all the more irresistible because they came unarmed ...'

Throughout its urban history, Hong Kong has been highly vulnerable to the unintended consequences of internal upheavals within China. 'The exodus,' Hughes darkly warned, 'was a dramatic warning of the mighty convulsions which can suddenly shake China at a time of national famine or distress, governmental confusion or expansion, [or] changing party or administrative policies.' And in case anyone gets too complacent, as closer examination of China's current top-level political shake-ups would indicate, we still are.

Until 1950, Chinese coming into Hong Kong from the mainland required no travel or identity documents, and only a tentative border control was in place.